#include <stdio.h>
#include <bitset>
#define NMAX 2000005
using namespace std;
bitset <NMAX> viz;
int n,rez;
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	int i,j;
	for (i=2; i*i<=n; i++)
		if (!viz[i])
			for (j=i*i; j<=n; j+=i)
				viz[j]=1;
	for (i=2; i<=n; i++)
		if (!viz[i])
			rez++;
	printf("%d\n",rez);
	return 0;
}